"Biochips" or micro arrays of binding agents, such as oligonucleotides, have become an increasingly important tool in the biotechnology industry and related fields. These binding agent micro arrays, in which a plurality of binding agents are deposited onto a solid support surface in the form of an array or pattern, find use in a variety of applications, including drug screening, oligonucleotide sequencing, and the like. One important use of biochips is in the analysis of differential gene expression, where the expression of genes in different cells, normally a cell of interest and a control, is compared and any discrepancies in expression are identified. In such assays, the presence of discrepancies indicates a difference in the classes of genes expressed in the cells being compared. While such information is useful for the identification of the types of genes expressed in a particular cell or tissue type, it does not provide information regarding the size of specific gene products expressed by the cell.
To obtain such information, one has to rely on the standard blotting protocols, e.g. Northern blotting and analogous procedures. In such procedures, a complex mixture of potential target compounds is first size separated and then transferred to a flexible support. A probe capable of detecting the compound of interest in then contacted with the size separated targets. Following a positive probe/target binding event, detection of the bound probe yields information regarding the size of the target. While such blotting procedures are capable of providing size information, formats being used to date are not suitable for use in high throughput analysis.
Because information concerning both the types of genes expressed and the size of the expressed products in a particular cell or tissue type are of interest in many applications, there is interest in the development of an array type device which can provide both types of information in a high throughput format.